1. Field of the Invention
The present invention relates to the preservation of acid-containing articles.
2. Description of the Background Art
Many acid-containing articles are vulnerable to destruction as a direct result of the acid contained therein. For example, most paper manufactured since the early nineteenth century contains acid. Such acid-containing paper deteriorates quite rapidly by yellowing, becoming increasingly brittle and finally disintegrating into dust, often within a matter of decades. In contrast, paper made without acid can last for centuries.
As aging, acid-containing paper increases in brittleness, it become more susceptible to damage during handling. Many documents of great value and importance, such as manuscripts, deeds, letters and the like, are printed on acid-containing paper. Destruction of such documents due to their acid content, represents a significant loss. In view thereof, numerous proposals have been made to prevent the age-related destruction of acid-containing paper documents, see, e.g., U.S. Pat. Nos. 3,703,353; 4,051,276; 4,522,843; 4,619,735; 4,808,433; 4,863,566; and 4,927,497.
One method utilized by the Library of Congress to conserve acid-containing paper documents is polyester film encapsulation. See, publication 1980 0-299-578, U.S. Government Printing Office. This method involves overlaying both sides of a document with polyester film sheets, and forming an envelope by sealing the polyester sheets around their edges ultrasonically or with tape. This U.S. Government publication indicates that documents that have been chemically deacidified and alkalized prior to polyester film encapsulation, can be preserved better than documents encapsulated without deacidification.
The most common methods used for deacidification of paper involve gaseous or liquid chemicals. However, chemical treatment of paper may be problematic for several reasons. The long term effects of any particular chemical treatment of paper are uncertain. With important paper documents disintegrating at an alarming rate, it may not be prudent to experimentally determine if a particular chemical will work to preserve the paper, or if it will destroy the document even further. The treatment of paper with chemicals generally is an irreversible process. The application of chemicals to paper is expensive and time consuming. Many of the chemicals are dangerous to use and environmentally hazardous. Additionally, documents which have been chemically deacidified are still vulnerable to air pollution and oxidative degradation by air.
While polyester film encapsulation of documents which have not been deacidified renders them resistant to destruction brought about by handling, the above-cited U.S. Printing Office publication 1980 0-299-578 indicates that encapsulated documents which have not been deacidified deteriorate at a faster rate than papers which have not been encapsulated. This is apparently due to the build up of degradative gases within the polyester envelope. Proposed solutions to this problem include providing air holes in the corners of the polyester envelope or leaving the envelope open along two edges thereof, to permit escape of degradative gases. However, providing holes in the envelope has been shown not to slow down the faster rate of degradation of encapsulated acid-containing paper. While deterioration of encapsulated acid-containing paper is slower inside a polyester envelope which is open along two edges, it has still been found to be faster than that observed for unencapsulated controls, as reported by Shahani, C. J., Research Officer, Library of Congress, in a letter to the editor, Abbey Newsletter, April 1986, p. 11.
Another proposal has been to encapsulate a sheet of alkaline paper along with the acid-containing paper to be preserved. While this has been reported as slowing the deterioration of acid-containing paper, the degradative reaction still continues with the acid-containing paper degenerating faster than non-acidic paper.
Other acid-containing articles subject to degradation brought about by their acid contents include articles of leather, certain textiles, photographs and the like.
There thus remains an urgent need in the art for improved systems and methods for preserving acid-containing articles.